Although the graph is intended for solid-fuel PHWRs, it implies that for molten salt reactors with on-line fuel processing one can operate the reactor longer without fissile top-up if the fertile is U238 than if it is Th232The thorium version won't even go critical below 1.8% fissile - three times natural uranium - never mind getting any amount of burnup !

How much longer then becomes a function of fissile breeding sustainability.Its pretty easy to get iso-breeding with loads of fissile (especially HEU) mixed with Th232, to produce U233.A bit tougher with Pu239 production from U238.In either case, fissile breeding sustainability is ONLY feasible with fuel processing.But fuel processing is considerably less complicated without thorium thrown into the LEU mix.

In India, uranium has importance mainly as the source of fissile from a long term view. After 34 years of denial of imports, the thinking will not go away early.Attempts are on to multiply the fissile through fast breeders but the aim has to be a thorium breeder. I have doubts if the Indian concept or the LFTR will fit the bill. I feel that the solution will be a fast (not the FLiBe view) MSR (not attempted by Indians). ORNL July 2011 paper has the right ideas. The Indians should move the fast converter program to MSR and then substitute the fertile to thorium, which needs more fissile and better neutron economy. It also gives longer core life and less of consumable poisons.The right beginning may come from China.

In a fast spectrum there are two decent choices:a) chloride on the 238U/239Pu cycle (as Taub, and more recently ORNL proposed)b) fluoride on the 232Th/233U cycle (as the French propose).

The latter will mean HEU in the core so it very much depends on the interpretation of anti-proliferation concerns. For some reason, no one seems to worry about pure 239Pu in the core as long as there is intense radiation (self-protected) but the same self-protection may not apply.

For some reason, no one seems to worry about pure 239Pu in the core as long as there is intense radiation (self-protected) but the same self-protection may not apply.

That reason has to do with the very low concentration of "pure 239Pu" in low-burnup fuel: you need a reactor capable of shuffling large quantities of fuel on-line, plus a large processing plant to handle the throughput.No commercial power reactor has that kind of capability -- and that includes Candu reactors, with their slow on-line robotic fuelling machines (handling hundreds of precision seals on high-pressure fuel channels).If you wait longer for more Pu to build up, then the product is no longer "pure 239Pu".Even with only a few thousand MWd/tonne burnup (Candu is ~7800 average), the SNF Pu is already "reactor grade" - similar to LWRs, with much higher burnup (66% Pu239 for Candu vs. 63% for LWR).

The comment "no one seems to worry about pure 239Pu" could just as well be applied to 239Pu produced in the rocks & soil on land everywhere, by cosmic ray neutrons hitting uranium commonly present in them: the concentration of "pure 239Pu" is simply not practically useable !

For some reason, no one seems to worry about pure 239Pu in the core as long as there is intense radiation (self-protected) but the same self-protection may not apply.

That reason has to do with the very low concentration of "pure 239Pu" in low-burnup fuel: you need a reactor capable of shuffling large quantities of fuel on-line, plus a large processing plant to handle the throughput.No commercial power reactor has that kind of capability -- and that includes Candu reactors, with their slow on-line robotic fuelling machines (handling hundreds of precision seals on high-pressure fuel channels).If you wait longer for more Pu to build up, then the product is no longer "pure 239Pu".Even with only a few thousand MWd/tonne burnup (Candu is ~7800 average), the SNF Pu is already "reactor grade" - similar to LWRs, with much higher burnup (66% Pu239 for Candu vs. 63% for LWR).

The comment "no one seems to worry about pure 239Pu" could just as well be applied to 239Pu produced in the rocks & soil on land everywhere, by cosmic ray neutrons hitting uranium commonly present in them: the concentration of "pure 239Pu" is simply not practically useable !

Ergo, if we have a molten salt reactor without such capability, it will be allowed to have HEU in the core. A fluoride reactor with, say, no online processing and a large salt volume (low fissile concentration), started up with reactor grade Pu?

At the very least, the adding of U238 (eg as depleted uranium) online to keep the denatured state seems useless, since operators can easily stop doing that.

Assuming that we could start it with a reasonable amount of 238U it would take a long time to evolve to 60% fissile which buys time for the international community to try to do something about it so I wouldn't say that it is pointless to put in 238U to start off. In general I don't think it is appropriate but there are regions of the world where that would be appropriate.

Assuming that we could start it with a reasonable amount of 238U it would take a long time to evolve to 60% fissile which buys time for the international community to try to do something about it so I wouldn't say that it is pointless to put in 238U to start off. In general I don't think it is appropriate but there are regions of the world where that would be appropriate.

I mean as in adding depleted uranium to keep the denatured state. It's silly. It burdens bonafide reactor operators and countries that are noncompliant will simply not add the depleted uranium. I understand the need for feed enrichment to be low enriched because the proliferation hazard comes from the enrichment facility.

For a converter reactor, a uranium only solution (pardon the pun) has some advantages. Very low enrichment needed for something like LiF-UF4, about 1% enrichment for the 490 Celcius melting eutectic with 27% UF4. Feed enrichment can be very low as well.

Of course that is not energy from thorium, and needs constant enrichment facilities. Which are the biggest proliferation hazard. Iran is not using reactors to make bombs, Iran is using enrichment facilities to make bombs, and today's most common reactor types require enrichment. In that sense any plan to use LEU is not proliferation proof at all, and it is much better to use reactor grade plutonium to startup thorium reactors and no enrichment facilities.

I mean as in adding depleted uranium to keep the denatured state. It's silly. It burdens bonafide reactor operators and countries that are noncompliant will simply not add the depleted uranium. I understand the need for feed enrichment to be low enriched because the proliferation hazard comes from the enrichment facility.

The thought here is that reactors have live status feeds. If a reactors status feed is cut-off or the reactor varies from its expected profile you have warning that someone is up to no good. If they were compliant up to that point then there will be several years to burn off the 238U before the fuel is very useful for a proliferator. Requiring continuous denaturing then provides a few years warning and a chance for some response.

I agree that enrichment facilities and more generally eliminating the market for enrichment services would be the best technical advance we could do to help with the anti-proliferation effort. In that vein, iso-breeders are quite attractive. Whether they are started with LEU20 or SNF/Pu is only a transient effect. For startup purposes I don't see alot of difference between startup on LEU20 or SNF/Pu as far as proliferation risk. Enrichment is the easiest path but Pu separation from spent fuel is a second path to separate fissile for weapons. So both the know-how and equipment for enrichment and the know-how and equipment for Pu separation represent some risk.

Breeders are necessary to burn U238 or thorium which, in turn, is necessary for energy security. The basic design has to be governed by availability, scaling and economy of power and operator safety. Non-proliferation has to be bracketed with material security and precautions against sabotage.My thinking, based on my own limited understanding, points to the final aims of fast MSR breeders burning uranium for those burdened with a lot of spent LWR fuel and thorium burning for those newly arriving like China and India.Recovered TRU/plutonium and 20% LEU can be starter fissile feeds.

Jagdish,We covered this before. There is ample fertile to go around and we use so little of it in a breeder or iso-breeder that we will NEVER use up all the existing mined uranium (depleted uranium stocks from enrichment) nor all the thorium byproduct of rare earth processing. So we should have free choice in using either one as best suits the reactor. The goal of using up all the waste uranium or thorium is both unattainable and not important.

So for the US we should feel free to pursue thorium or uranium as the fertile feed. Similarly, 238U if used in a (iso)breeder is plentiful and even India should consider it as a basic fuel if that is the reactor style they prefer. Fuel availability for either 232Th or 238U is not an issue - it is only an issue if you have a 235U burner - and then especially if access to enrichment is constrained.

There is no reason we couldn't cooperate and come up with a design that works for both of us.

Thorium's Potential in Nuclear Power Developmenthttp://www.iaea.org/OurWork/ST/NE/NEFW/ ... pment.htmlThe IAEA, in cooperation with Indian Rare Earths Limited (IREL) organised an international Technical Meeting on ‘World Thorium Resources’ on 17 – 21 October 2011, in Thiruvananthapuram, India. The meeting was supported by Atomic Minerals Directorate for Exploration and Research, Hyderabad, and the University of Kerala, Thiruvananthapuram.

Thorium as nuclear fuel is dependent on availability of fissile feed. Imported uranium could help meet the requirement. It could be reactor grade plutonium recovered from reprocessing the used fuel or even 20% LEU. Current status is the development of fast breeders to multiply the availability of plutonium.

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